The incandescent lamp has been the mainstay of illumination for well over one hundred years. It is simple to construct, relatively inexpensive to manufacture, easily transportable, and has a strong emission in the yellow-green portion of the spectrum. Numerous techniques have been employed over the years to modify the black-body emission of the hot filament. For example, U.S. Pat. No. 2,405,261 suggests adding a layer of a chrome green enamel to a clear enamel to modify the light output in the 500 to 560 nm range. U.S. Pat. No. 2,759,119 suggests adding a phosphor material to the interior of the lamp envelope, such phosphor material to be energized by the electron emission and the ultraviolet radiation from the tungsten filament to produce luminescence in the green portion of the spectrum. U.S. Pat. No. 5,118,985 suggests the inclusion of a phosphor material that absorbs radiation below 500 nm and emits radiation above 500 nm to provide an improved bugfoiler lamp.
Recently, incandescent lamps having an enriched emission in the blue region of the spectrum have been introduced for use in household applications, so-called “daylight” incandescent lamps. One of the methods for achieving this relative enhancement in the blue region has been to provide a blue-tinted glass for the envelope, e.g., a glass employing an additive of neodymium in the form of Nd2O3. Another technique, disclosed in U.S. Pat. No. 6,670,768, employs a coating employing a blue cobalt aluminate, CoAl2O4, pigment. Both of these techniques increase the relative proportion of blue in the emission spectrum of the lamp by absorbing a significant portion of the yellow light emitted by the filament